32nd International Symposium on Lattice Field Theory (Lattice 2014)

Session

Theoretical Developments

5

24 Jun 2014, 14:15

Columbia University

Conveners

Theoretical Developments: Parallel 3E

• Michael G Endres (MIT)

Theoretical Developments: Parallel 4E

• Herbert Neuberger (Rutgers)

Theoretical Developments: Parallel 5E

• Agostino Patella (CERN and Plymouth University)

Theoretical Developments: Parallel 6E

• Stefan Sint (Trinity College Dublin)

Theoretical Developments: Parallel 7E

• Hidenori Fukaya (Osaka University)

Theoretical Developments: Parallel 8E

• Ulli Wolff (Humboldt University, Berlin)

46. Polyakov Loop Correlations at Large N

Prof. Herbert Neuberger (Rutgers)

24/06/2014, 14:15

Theoretical Developments

Talk

The topic of the presentation is the two-point single-eigenvalue distribution correlation function of Polyakov loops in the confined phase of four dimensional SU(N) YM theory at large N.

355. TEK twisted gradient flow running coupling

Liam Keegan (CERN)

24/06/2014, 14:35

Theoretical Developments

Talk

We measure the running of the twisted gradient flow coupling in the Twisted Eguchi-Kawai (TEK) model, the SU(N) gauge theory on a single site lattice with twisted boundary conditions in the large N limit.

341. Testing volume independence of large N gauge theories on the lattice

Prof. Antonio Gonzalez-Arroyo (Instituto de Fisica Teorica UAM/CSIC)

24/06/2014, 14:55

Theoretical Developments

Talk

We present the results of our direct precision test of volume independence for SU(N) Yang-Mills theory on the lattice with Wilson action. Wilson loop expectation values at large N are obtained by extrapolation and its finite volume dependence examined for different boundary conditions.

234. Temperature dependence of the chiral condensate in the Schwinger model with Matrix Product States

Dr Hana Saito (DESY Zeuthen)

24/06/2014, 15:15

Theoretical Developments

Talk

Tensor network methods form a family of efficient techniques of approximating quantum states. Their successes in quantum many-body physics have inspired their use for lattice gauge theories. We employed one of the tensor network techniques, called Matrix Product States, to investigate the Schwinger model in the Hamiltonian formulation. In this talk, we show our results for the temperature...

96. Grassmann Tensor Renormalization Group Study of Lattice QED with Theta Term in Two Dimensions

Dr Yuya Shimizu (RIKEN)

24/06/2014, 15:35

Theoretical Developments

Talk

The tensor renormalization group is one of the successful methods to tackle systems whose action is complex, though the practical calculations in higher dimensions is beyond the reach of current computer facilities. The Grassmann tensor renormalization group is a generalization to systems including fermions. As a pilot study toward lattice QCD, we apply it to two-dimensional lattice QED and...

386. Causal Space-Time on a Null Lattice with Hypercubic Coordination

Dr Martin Schaden (Rutgers University)

24/06/2014, 16:30

Theoretical Developments

Talk

I discuss the discretization of causal space-times on a topological lattice of events with hypercubic coordination whose links are light-like. Conditions that ensure this lattice is the discretization of a causal manifold are derived. They are encoded by a local topological lattice theory which has a particularly simple and appealing form when null-coframes are represented by spinors.

104. Triviality of ${\varphi }_4^4$ in the broken phase revisited

Prof. Ulli Wolff (Humboldt University, Berlin)

24/06/2014, 16:50

Theoretical Developments

Talk

We define a finite size renormalization scheme for ${\varphi }^4$ theory which in the thermodynamic limit reduces to the standard scheme used in the broken phase. We use it to re-investigate the question of triviality for the four dimensional infinite bare coupling (Ising) limit. The relevant observables all rely on two-point functions and are very suitable for a precise estimation with the...

254. Lattice study on diquark properties

Zhaofeng Liu (Institute of High Energy Physics)

24/06/2014, 17:10

Theoretical Developments

Talk

Two point functions of diquarks are calculated in the Landau gauge on the lattice with overlap fermions on 2+1-flavor domain wall fermion configurations. Masses of diquarks with spin 0 and 1 in the color anti-triplet representation are extracted. Pion mass dependence of the mass difference between the bad and good diquarks are studied.

120. Induced QCD with Nc auxiliary bosonic fields

Dr Bastian Brandt (University of Regensburg)

24/06/2014, 17:30

Theoretical Developments

Talk

We investigate an alternative lattice discretization of continuum SU(Nc) Yang-Mills theory in which the self-interactions of the gauge field are induced by a path integral over Nc auxiliary bosonic fields which are coupled linearly to the gauge field. In two dimensions there exists an analytic proof that the new discretization reproduces Yang-Mills theory in its non-perturbative continuum...

329. Matrix product states for gauge field theories

Mr Boye Buyens (University Ghent), Dr Karel Van Acoleyen (Ghent University)

24/06/2014, 17:50

Theoretical Developments

Talk

We consider the matrix product state formalism for the simulation of Hamiltonian lattice gauge theories. To this end, we define matrix product states which are manifestly gauge invariant. As an application, we study 1+1 dimensional one flavor quantum electrodynamics, also known as the massive Schwinger model. We are able to determine very accurately the ground state properties and one-particle...

7. Prepotential Formulation of Lattice Gauge theories

Dr Indrakshi Raychowdhury (Institute of Mathematical Sciences, Chennai, India)

25/06/2014, 09:00

Theoretical Developments

Talk

Within the Hamiltonian formulation of Lattice gauge theories, prepotentials, belonging to the fundamental representation of the gauge group and defined locally at each site of the lattice, enables us to construct local loop operators and loop states. Within this prepotential approach one gets mass gap analytically in some approximations in the weak coupling limit of the theory.

102. Lattice Hamiltonian approach to the Schwinger model

Mr Marcin Szyniszewski (Lancaster University, The University of Manchester)

25/06/2014, 09:20

Theoretical Developments

Talk

We employ exact diagonalization with strong coupling expansion to the massless and massive Schwinger model. For the massless case, this allows us for a high accuracy continuum limit estimation of the ground state energy and scalar and vector mass gaps with precisions of the order of one part per billion or better. Furthermore, we investigate the chiral condensate and compare our calculations...

227. Update on staggered Wilson fermions

David Adams (Nanyang Technological University)

25/06/2014, 09:40

Theoretical Developments

Talk

An update on our ongoing research on staggered Wilson fermions (a 2-flavor staggered version of Wilson fermions) will be given. Previously we found that this formulation is 4-6 times more efficient than usual Wilson fermions for inverting the Dirac matrix in quenched backgrounds of a 16^3 x 32 lattice at beta=6. Further results for 20^3 x 40 lattices will be reported which reveal that the...

8. Pion masses in 2-flavor QCD with $\yen eta$ condensation

Prof. Sinya Aoki (Kyoto University)

25/06/2014, 10:00

Theoretical Developments

Talk

We investigate some aspects of 2-flavor QCD with $m_u\yen not=m_d$ at low-energy, using the leading order chiral perturbation theory including anomaly effects. While nothing special happens at $m_u=0$ for the fixed $m_d\yen not=0$, the neutral pion mass becomes zero at two critical values of $m_u$, between which the neutral pion field condenses, leading to a spontaneously CP broken phase, the...

54. Spectrum of the staggered Wilson Dirac operator in quenched lattice QCD backgrounds

Mr Christian Zielinski (Nanyang Technological University, Division of Mathematical Sciences)

25/06/2014, 10:20

Theoretical Developments

Talk

Results for the spectrum of the staggered Wilson Dirac operator in quenched backgrounds (beta = 5.8 and 6) are presented for a range of different lattice sizes up to 16^3 x 32. Significant improvement in the physical branch of the spectrum is observed for the larger lattices. The results are also compared with spectrum results for the usual Wilson Dirac operator in the same backgrounds.

328. Conformal Lattice Field Theory on Spherical Manifolds

Dr Richard Brower (Boston University)

25/06/2014, 11:10

Theoretical Developments

Talk

Lattice radial quantization is a nonperturbative method especially suited to numerically solve Euclidean conformal field theories. Tests are made for the critical surface of the phi 4th theory at the Wilson-Fisher critical point in 3D on R x S2 and in 2D on the Riemann sphere. Simplicial lattice using the Finite Element Methods (FEM) or Regge calculus discretization are need to...

277. Blocking versus Sampling

Yannick Meurice (University of Iowa)

25/06/2014, 11:30

Theoretical Developments

Talk

The idea of blocking in configuration space has played an important role in the development of the RG ideas. However, despite being half a century old and having had a huge intellectual impact, generic numerical methods to perform blocking for lattice models have progressed more slowly than sampling methods. Blocking may be essential to deal with near conformal situations. Typically,...

179. Topologically restricted measurements in lattice sigma-models

Dr Urs Gerber (Instituto de Ciencias Nucleares - Universidad Nacional Autonoma de Mexico)

25/06/2014, 11:50

Theoretical Developments

Talk

We consider models with topological sectors and difficulties with their Monte Carlo simulation. In particular, we are concerned with the situation where a simulation has a very long auto-correlation time with respect to the topological charge. In such cases, reliable numerical measurements are only possible within single topological sectors. The challenge is to assemble such restricted...

177. Hadron masses from fixed topological simulations: discussion of parity partners and SU(2) Yang-Mills results.

Arthur Dromard (Goethe Universität, Frankfurt am Main)

25/06/2014, 12:10

Theoretical Developments

Talk

Lattice QCD simulations tend to become stuck in a single topological sector at fine lattice spacing or when using chirally symmetric overlap quarks. In such cases physical observables differ from their full QCD counterparts by finite volume corrections, which need to be understood on a quantitative level. We discuss extensions of existing relations from the literature between correlation...

115. Non-perturbative renormalization of the energy-momentum tensor in SU(3) Yang-Mills theory

Dr Michele Pepe (INFN)

25/06/2014, 12:30

Theoretical Developments

Talk

We report on an ongoing project of determining non-perturbatively the finite renormalization constants of the energy-momentum tensor in the SU(3) Yang-Mills theory. We compute them by imposing on the lattice suitable Ward Identites at finite temperature and volume in presence of shifted boundary conditions. We present accurate preliminary numerical data for values of the bare coupling g_0^2...

239. Topology density correlator on dynamical domain-wall ensembles with nearly frozen topological charge

Hidenori Fukaya (Osaka University)

25/06/2014, 12:50

Chiral Symmetry

Talk

Global topological charge tends to decorrelate very slowly or to even freeze on fine lattice simulations, while local topological fluctuations are expected to survive and lead to correct physical results as long as the volume is large enough. We investigate this issue on the recently generated configurations including dynamical domain-wall fermions at a=0.08 fm and finer. We utilize the...

186. Optimisation of Quantum Evolution Algorithms

Prof. Apoorva Patel (Indian Institute of Science, Bangalore, India)

26/06/2014, 14:15

Algorithms and Machines

Talk

A specific unitary evolution operator can be constructed in many different ways, corresponding to different Hamiltonian trajectories between the desired end-points. An optimal trajectory can then be selected to make the evolution have the best computational complexity and control over errors. Using Grover's quantum search algorithm as an explicit example, it is shown that the complexity...

350. Tensor renormalization group study of the 2d O(3) model

Judah Unmuth-Yockey (University of Iowa)

26/06/2014, 14:35

Algorithms and Machines

Talk

We study the two-dimensional O(3) model on the lattice using the Tensor Renormalization Group (TRG) approach, with the goal of understanding asymptotic scaling at both the large volume, and large beta limit. Harmonic analysis on the Boltzmann weight introduces a sign problem into the partition function, which makes the model difficult to study with the Worm Algorithm. The TRG...

288. Energy-momentum tensor on the lattice and Wilson flow

Dr Agostino Patella (CERN and Plymouth University)

26/06/2014, 14:55

Theoretical Developments

Talk

The energy-momentum tensor in lattice gauge theories requires renormalization because of the breaking of Poincare' group. The Wilson flow can be used in principle to set up non-perturbative, well-defined and, possibly, practically convenient strategies to define a properly renormalized energy momentum tensor. I will present some preliminary data in this direction.

215. String tension from smearing and Wilson flow methods

Prof. Masanori Okawa (Hiroshima University)

26/06/2014, 15:15

Theoretical Developments

Talk

Last year, we proposed a new method to extract string tension using 4-dimensional smearing method (PL B718 (2013) 1524). In this talk we first show that results using smearing method are equivalent to those obtained by Wilson flow once the time step \epsilon is sufficiently small. We then demonstrate the practical advantage of our method by applying it to the calculation of Creutz ratio in...

173. Tree level improvement of the gradient flow

Dr Daniel Nogradi (Eotvos University)

26/06/2014, 15:35

Theoretical Developments

Talk

The Yang-Mills gradient flow is considered in lattice perturbation theory at leading order of the gauge coupling and O(a^8) in the lattice spacing. Improved actions are incorporated for the gauge action, the flow itself and the observable for E(t). The results lead to a setup with O(a^6) improvement at tree level.

107. How to reduce O(a^2) effects in gradient flow observables?

Stefan Sint (Trinity College Dublin & NIC@DESY-Zeuthen)

26/06/2014, 15:55

Theoretical Developments

Talk

The gradient flow has become a very useful tool both for scale setting and for defining suitable finite volume schemes for the gauge coupling. However, surprisingly large cutoff effects have been observed in some cases. We here investigate these effects at leading order in perturbation theory and reproduce qualitative features that have previously been observed in the context of scale setting....

338. Locally smeared operator product expansions

Dr Christopher Monahan (College of William and Mary)

26/06/2014, 16:15

Theoretical Developments

Talk

We propose a new ``smeared'' operator product expansion (sOPE) in which the set of local operators in the OPE are replaced by their locally smeared counterparts, generated by the gradient flow. The flow time, or smearing, parameter serves as a regulator for both Wilson coefficients and operator products. Matrix elements determined nonperturbatively on the lattice using smeared degrees of...

133. A construction of the Schrodinger Functional for Möbius Domain Wall Fermions

Ms Yuko Murakami (Hiroshima University)

27/06/2014, 14:15

Theoretical Developments

Talk

We investigate the universality of Möbius Domain Wall Fermions (MDWF) in the Schrödinger Functional (SF) scheme at tree level. We introduce the SF boundary condition to the MDWFs by adding a temporal boundary operator. When the fifth dimensional parameters of the MDWF are a constant, this construction seems to be natural according to the Luescher’s universality prescription for the overlap...

48. Crank-Nicolson discretization scheme and lattice fermions

Prof. Artan Borici (Uiversity of Tirana)

27/06/2014, 14:35

Chiral Symmetry

Talk

It is well known that Crank-Nicolson discretization scheme is second order accurate in time. Its application in the case of the Dirac operator leads to a lattice theory with reduced doublers and broken parity. Adding a 3-space Wilson term one obtains a single fermion which is second order accurate in time. In the case of an imaginary term the doubler degeneracy is lifted and the ground state...

41. Fermion Mass Generation without a chiral condensate

Mr Venkitesh Ayyar (Duke University)

27/06/2014, 14:55

Chiral Symmetry

Talk

Massless fermions can become massive due to interactions through the mechanism of Spontaneous Symmetry Breaking (SSB). This mode of mass generation is popular and has been used in the Standard Model. Here, we explore the possibility of fermions acquiring a mass through interactions, but without SSB.\\ We consider a fermion system on a cubical lattice and introduce an on-site four-fermion...

12. The Hadronic Spectrum and Confined Phase in (1+1)-Dimensional Massive Yang-Mills Theory

Dr Axel Cortes Cubero (City University of New York)

27/06/2014, 15:15

Theoretical Developments

Talk

Massive Yang-Mills theory is known to be renormalizable in 1+1 dimensions. The gluon mass is introduced by coupling the gauge field to an SU(N) principal chiral nonlinear sigma model. The proof of renormalizability relies on the asymptotic freedom of the sigma model. However, renormalization forces the gluon mass to infinity. The continuum theory is in a confined phase rather than a Higgs...